Method and apparatus for evaporation



Aug. 5, 1941. L 3, BLACK v 2,251,317

I METHOD AND APPARATUS FoR EVAPORATION Filed Jan. 25, 1959 2 Sheets-Sheet 1 -g- 5, 1941- 0 LG. BLACK 2,251,317

METHOD AND APPARATUS FOR EVAPORATION Filed Jan. 25, 1939 2 Sheets-Sheet 2 Patented Aug. 5, 1941 UNITED} STATES- PATENT OFFICE METHOD ann'armasrus FOR EVAPORATION Leroy G. Black, Trona, Calif., assignor to American Potash & Chemical Corporation, Trona, Calm, a corporation of Delaware Application January 25, 1939, Serial No. 252,785

,10 Claims. (01. 159-45) and, while including features applicable generally to evaporating processes and apparatus, is especially useful in cases where evaporation is accompanied by crystallization of a solute from a solution.

In the operation of evaporators or evapora tive crystallizers on solutions, especially those operations in which the crystallization of a solute occurs during the evaporation, solid-deposits are formed on the exposed surfaces within the vapor space and vapor lines, and tend to accumulate and serlouslyreduce the capacity of the apparatus. This trouble occurs especially on the walls, at the liquor level; also, above the liquor level, and even in the vapor lines. Such accumulation will build up and form an annulus of salt just above the liquor level, which seriously reduces the exposed liquor surface and may eventually entirely close over said surface. These accretions reduce the capacity of the apparatus and sometimes break off in large chunks which plug liquor lines and interfere with pump operation. 1

The formation of solid deposits on the exposed surfaces within the evaporator may be prevented or the accumulated solids removed by applying to the afllicted surfaces a solvent for the solids. Such solvent is hereafter referred to as a wash liquor or fluid, although the same may act either to dissolve thesolids, mechanically displace the same, or partially dissolve and partially displace the same. Attempts to apply such wash liquors to the exposed surfaces, for example, by stationary sprays have proved unsatisfactory in practice for the reason that thewash liquor tends to form channels on the surfaces, upon which it impinges, and to flow down the wall in rivulets. Between the rivulets the solids will collect and build up. This is particularly true when the quantity of wash fluid is held to a minimum to avoidexcessive dilution of the solution being concentrated. Heretofore, the art has had no satisfactory method or 'apparatus for removing salt deposits from the exposed surfaces of evaporators or for preventing the formation of such deposits on such surfaces, for the reason that the processes and apparatus heretofore used for that purposehave either failed to remove the salt deposits, or-hav'e required the introduction into the evaporator of undesirable quantities of wash liquor which interfere with the eiliciency of the evaporating operation. I

It is a general objector the present invention to provide a method and apparatus for evaporating liquids, particularly when the evaporation is accompanied by crystallization, which method and apparatus are capable of preventingaccumulation of salt deposits on the exposed sur-' faces of the evaporator without requiring the introduction into the evaporator of an undesirable quantity of wash liquor.

In accordance with the present invention, the accumulation of solids on the exposed surfaces of the evaporator is prevented by completely covering the'upper zone'of the exposed surfaces with a wash liquor and allowing the liquor so applied to run down so as tocover the exposed surface completely. This complete coverage is attained by supplying the wash liquor to the exposed surface from a revolving member which distributes it by preferably flinging the. liquor against the area subject to the deposition of solids. The wash liquor may be supplied directly to the rotating member, or the rotating member or flinger may intercept a falling stream of wash liquor in such a manner as to catch the same and carry or fling the wash liquor against the surface, subject to the deposition of solids. By the method and apparatus of the present invention 'a deposit of wash liquor is continuously and repeatedly laid down over the exposed surface,

thus wetting the entire surface. Likewise, be-v cause the flinger rotates around the vertical axis of the evaporator at a uniform rate, the wash liquor supplied to it is distributed evenly and uniformly to all portions of the surface adjacent the ends of the flinger. This is equally true when the quantity of wash liquor used is large or small, and consequently the improved method and means of this invention is efllcient-and satisfacployed using fluid. l

While the method and apparatus of the present invention may be designed so as to employ Y to the evaporator.

as the wash'liquor a liquid supplied from without the evaporator either entering under pressure through the rotating or flinging apparatus, or in the form of a stream of droplets intercepted by the flinging apparatus, the method and apparatus of the present invention is especially valuable when it employs as the wash liquor a condensate from the evaporating process. In certain processes of evaporation the evaporated vapors are condensed and a portionvor' all thereof returned The condensate condensed within the evaporator falls more or. less like droplets of rain, and, by so arranging the flinger of the apparatus as to intercept such droplets,

' the same may be very satisfactorily distributednecessity of introducing outside washing fluids is avoided with consequent benefit to the evapcrating process.

The present invention, further objects and advantages thereof, lwill be more fully understood from the following description of a preferred form or forms of methods and apparatus embodying the present invention. For this purpose, I have described a preferred form or forms of the invention in connection with the accompanying drawings, in which- Figure 1 is a vertical section of a refluxing type vacuum crystallizer embodying the present invention, broken in the view so as to particularly shorten the liquor-holding portion thereof.

Figure 2 is a section on the line 2-2 of Figure 1.

Figure 3 is a side view of one of the flinger blades. I

Figure 4 is an end view of the flinger blade.

Figure 5 is a fragmentary vertical section with the vapor space of an evaporator showing a modified method and means for supplying wash liquor.

Figure 6 is a view of a modified form of flinger blade.

While not confined to such use, the apparatus of the present invention is particularly useful in the operation of evaporative crystallizers, for

example, vacuum crystallizers, and, as the difficulty sought to be overcome by the present invention is well illustrated in the case of vacuum crystallizers, I have shown the preferred form of the invention as applied to such vacuum crystallizing apparatus.

Referring to Figure 1 of the drawings, I have shown an evaporative' crystallizer which comprises a right cylindrical outer shell i, of steel or other suitable material. A bottom enclosure 2 of conical section and an arched top 3 close off the ends of the shell I and form therewith a bottom zone 4 for. holding a body of liquor to be evaporated and an upper zone 5 or vapor space. Solution to be treated is introduced through an inlet 6 near the bottom of the shell I and in continuous operation is removed through an overflow outlet 1. The vapor space 5 is of a suflicient size to prevent undue splashing of the liquor into the outgoing vapor line l5. The vapor linel5 and other accessories, such as evacuating and condensing means (not shown) should be of sufficient size to accommodate the maximum quantity of vapor to be taken from the surface of the boiling liquor.

Operation of the crystallizer is started by fllling it with solution and maintaining a pressure within the vapor space which is lower than the vapor pressure of the solution. This may be accomplished in any of a variety of ways, as with a barometric or surface condenser to which the vapor line l5 leads, or by means of a boosterejector operating in conjunction with the vapor line [5. Non-condensible gases must also be removed continuously from the vapor space 5. During operation, there will be a continuous stream or current of vapors passing from the liq.- uor body into the vapor space 5 and then nto the outgoing vapor line l5.

In order to keep the walls above the liquor together with various .1

level (i. e, the walls of the vapor space free of solids, I supply a washing fluid to a novel form of distributor, which I have termed a flinger, revolving within the vapor space 5. The flinger is designed to rotate in a path or plane which is more or less normal to the surface area on which the washing fluid is to be distributed. Fundamentally, the flinger may be any rotatable or rotating member or device to which washing fluid can be supplied and which will distribute the fluid over the surface area beyond its outer ends during rotation. The action desired is that of subdividing the fluid and throwing it outward onto the desired surface areas continuously in a moving path around the crystallizer or evaporator. The rotation of the flinger assures the distribution thereof in a moving path which continuously, progressively, and successively covers the wall area.

In keeping with the above basic characteristics of the flinger, the particular design used may be of several types. My preferred form of distributor or flinger is actuated or rotated independently and the washing fluid supplied in dispersed form thereabove. In this form, the flinger has a plurality of blades which extend close to the surface which is to be washed, and rotates in a plane which is more or less normal to said surface. Thus, for example, in washing the walls of the vapor space of an evaporator or evaporative crystallizer, I mount the flinger 8 to rotate in a horizontal plane within the vapor space andat the upper level of the surface area to be washed. The mounting by which the flinger is positioned within the vapor space is any rigid construction which permits a source of power to be transmitted to the flinger for rotating it. I show the flingermounted on a shaft which has a lower bearing 2| with supports 2| attached to the walls of the vapor space and an upper bearing 22 outside. and on top of the evaporator. Shaft 20 extends beyond the crystallizer through a mercury seal 23 which prevents air leaks into the vapor space 5 around the shaft. Rotation of the flinger is effected by a motor 24 connected to the upper end of the shaft through a suitable gear reducer 25, i

The flinger, per se,, comprises a number "of blades l6 fastened to or mounted on a central hub I! which is keyed to the rotating shaft 20. I prefer to construct the entire flinger of light material and, therefore, provide an outer band or rim I!) which encircles and joins the outer ends of the blades l6. Each blade has a small ear H3 at its outer end which is fastened to the rim. The rim is relatively narrow and extends only a short distance below the ears l8. It serves both to strengthen the structure and to maintain the blades in a predetermined spaced relationship.

In operation, the flinger is rotated by the motor operating through the gear reducer and washing fluid is supplied so as to fall freely in the vapor space above the flinger. Drops of iluid are preferred to a stream as they facilitate the diversion of the fluid to the walls. The diops fall onto the blades l6 and are intercepted thereby, and the rotation of the blades causes the fluid to be thrown outward by centrifugal force which otherwise from the lower edges of the bladea collects on the launders and flows.

along their to the ends of theblades. By mak-Y" in: the outer band or rim ll narrow, as much as possible of the end of the blade, and especially the end of the launder, is left with a free path tothe walls.

Washing fluid should be supplied, as no above, so as to fall freely in the vapor space above the flinger. Preferably also it falls in a sub divided form dispersed over a considerable proportion of the zone traversed by the flinger. This may be done in various ways, one of which is showndn Figure 5. The washing fluid entersfrom the outside through a line 9 which is fur- Generally, there will be sumcient condensate to I keep the walls clean, though the quantity is not actually large in comparison with the volume of Y solution being cooled.

nished with a spray nozzle ll capable of directing a mist or rainstorm of drops which will fall onto the blades of the flinger ll. Withthisform of ing fluid the quantity supplied, rateof introduction, etc., may, of course, be controlled by means apparatus for and method of supplying the washof valves or other regulating means from the outside. The temperature of the fluid supplied may be that of any suitable liquor available and might be above or below that being maintained in the evaporator, unless special steps are taken to regulate said temperature. Since an unfavorable temperature difference between the washing fluid and that of the main body of liquor within the evaporator is to be avoided, I prefer to supply ,the fluid for washing essentially at or close to the temperature of the liquor body.

This may be readily accomplished by condensing vapors within the, vapor space of the evaporator above the flinger and allowing the .con-

densate to fall to the flinger. The condensate will be automatically close to the temperature within the vapor space and the temperaturebalance in the system is little disturbed by use of condensate, as the washing fluid. In a system using only refrigeration to condense the vapors,

part of the refrigerant may be supplied to a condenser within the vapor space,- and the total refrigeration load isrnot changed appreciably.

In Figure 1, refrigerant is supplied to a surface condenser l2 through a line l3 and withdrawn through line it. Condensate forms on the surface of the condenser and falls as a rainstorm of drops to the blades of the flinger.

In some processes, removal of solvent, 1. e. concentration, is a prime function of the operation and addition of solvent, e.g return of condensate,

must be limited then to the least quantity which will preserve the walls free of solids. The condenser for such systems is preferably designed to allow free access of the vapors and non-condensible gases to the outgoing vapor line l5, while condensing the limited quantity of vapors needed for the cleaning condensate. In particular, the condenser should have a, design and location which will avoid causing short-circuiting of the ,non-condensible gases.

In other processes, concentration of the crys-' tallizing solution is undesirable, usually because it causes precipitation of some contaminating substance. Evaporative cooling of such systems has been carried out by prediluting the solution 'by an amount equivalent to the solvent removed intercepted by all the blades is at least as great as the available quantity. This is the arrangea Only that quantity or washing fluid introduced from the outside, or condensate from condenser 12, need be intercepted by the blades of the flinger as will maintain the walls free of 501105; Obviously, however, it will be preferable to intercept as much fluid as is available, 1. e., as can be or is supplied above the flinger. A valuable feature of my invention is the ease with which the flingcr can be designed to collect any desired proportion of the condensate and to do so without appreciably interfering with the normal upward flow of the vapors to the condenser i2. Each blade is given a twist or pitch about the central hub i'l so that the lower edges of the leading faces lead, as the flinger is ro-' tated. The degree of pitch imparted to the blades is predetermined so that the upward component of the rotating blades is of thesame order of magnitude, and preferably the same as the upward rate of flow of the vapors. I prefer to rotate the blades slowly at, say, from 25-40 R. P. M.,.and the pitch is selected so that the blades do not react appreciably: on the vapor stream at that speed. Other'rotation rates may be used, however, with the degree of pitch being' selected accordingly. Normally, I prefer to operate the flinger so that no work, either positive or negative, is done with respect to the rising vapors, but in some cases the flinger, may be caused to have a pumping effect, increasing the rate of travel of the vapors to the condenser.

Operating the flinger so that there is no reaction onrthe' vapor stream has the furtherade vantage that particles shot off from the boiling ing fluid to seep through and keep the solids in a slushy condition, thereby preventing accumulation thereof. Such a perforated blade is shown in Figure 6, 2 1 indicating the perforations.

Rate of rotation also affects the quantity of condensate interceptedby the flinger, the latter being controlled also by the depthkof' the blades, the distance of the flinger from the point at which the washing fluid begins its descent thereto, and the number of blades. All of the condensate will be intercepted when the fields of influence of the adjacent blades of the flinger slightly overlap. By fields of influence, I mean the amount of falling fluid which is intercepted and dispersed .by a blade in .one revolution and complete coverage of the available fluid occurs when the blades are'deep enough so that, at the rotation rate chosen, the fluid which can be ment I prefer and have shown, though other designs may be preferred in some cases. I also prefer to locate the flingerclose to. the source of fluid supply and the latter near the top of .space.

the vapor space, so that. condensate will be sprayed over the wall near the top of the vapor liquor body and all parts of the exposed wall area are continuously washed and kept free of solids.

I have found the process and apparatus of Condensate then runs downward to the the present invention to be most satisfactory in removing or preventing salt accretlons on the exposed surfaces of an evaporator. Moreover,

this method and apparatus by distributing the washing liquor uniformly over the exposed surfaces prevents the formation of rivulets and al-' vapors, some being faster and others slower.

Since the flinger is designed toj avoid reacting on particles moving at the average velocity of the vapors, solids traveling either faster or slower than the average will contact a blade of the flinger. Such particles will either be thrown off with the condensate or may collect for a time and then drop off. If the quantity of solids which collect on the blades in excessive when .the filnger is rotating at the proper speed for the vapors, then, as already noted, perforating the blades will permit some condensate to seep through and keep the lower sides moist and free of solids.

In the embodiment of the invention shown, I have described means for distributing washing fluid over the exposed wall surfaces of the Y vapor space of an evaporator. The invention is also useful and readily adaptable for distributing the fluid within other parts of evaporative'equipment carrying vapors and subject to the deposition and accumulation of solids. Vapor lines, especially those portions nearest the vapor space,

are sometimes aiilicted with accumulations of solids, especially when a refluxing condenser is not used in the vapor space. Washing fluid can be supplied to suitable means for distributing the condensate positioned. within the aiiiicted zone to .obviate such trouble. It will thus be appreciated and understood that my invention is useful in any case where a fiinger can rotate in a zone in which solids tend to accumulate. I have, therefore, used the term vapor space= in the claims to refer broadly to any vapor-carrying member or zone.

In certain applications of the invention solids may tend to stick to the propeller or filnger blades. This may be overcome in certain cases by making the blades of some plastic .material or covering them with a flexible material which will cause the solids to break off and retard their accumulation on the flingers.

While the particular apparatus and process herein described is well adapted to carry out the principles and objects of the present invention, it is to be understood that various modifications and changes may be made all coming within the scope of the present invention, and this invention includes all such modifications and changes as come within the appended claims.

I claim:

1. In combination in an evaporator having a portion for holding a body of solution to be evaporated and a vapor space above said portion, means for condensing within said vapor space atleast a portion ofthe vapors produced by evaporation, a revolving deflector mounted to rotate within said vapor space below said condensing means and to distribute condensate from said condenser onto exposed surfaces within said vapor space, and means to rotate said device.

2. In combination in an evaporator having a portion for holding a body of solution, a vapor space above said portion, an outlet for gases and vapors'from said vapor space, and means for maintaining a pressure within said vapor space such that evaporation will occur from the body of solution, a surface condenser located within the vapor space, a fan disposed to rotate in a horizontal plane below said condenser, and means to rotate said fan whereby condensate from said condenser is intercepted by the fan and distributed onto exposed surfaces within said vapor space. Y

3. In combination in an evaporator having a portion for holding a body of solution, a vapor space above said portion, an outletfor gases and vapors from said vapor space, and means for maintaining a pressure within said vapor space such that evaporation will occur from the body of solution, a surface condenser located within the vapor space, a fan disposed to rotate in a horizontal plane below said condenser, and

means to rotate said fan whereby condensate from said condenser is intercepted by the fan and distributed onto exposed surfaces within said vapor space, the rate of rotation and pitch of the blades of said fan being such that the reaction component on the vapors is at least as high as the normal rate of rise of the vapors.

4. In combination in an evaporator having a portion for holding a body of solution, a vapor space above said portion, an outlet for gases and vapors from said. vapor space, and means for maintaining a pressure within said vapor space such that evaporation will occur from the body of solution a surface condenser located within the vapor space, a fan disposed to rotate in a horizontal plane below said condenser, and means to rotate said fan whereby condensate from said condenser is intercepted by the fan and distributed onto exposed surfaces within said vapor space, the rate of rotation, depth of blades and number of blades of saidfan being such that essentially all of the condensate from said condenser is intercepted by the fan during rotation.

5. In combination in an evaporator having,

a portion for holding a body of solution, a vapor space above said portion, an outlet for gases and vapors from said vapor space, and means for maintaininga pressure within said space such that evaporation will occur from the body of solution, a surface condenser located within the vapor space, a perforated fan disposed to rotate in a horizontal plane below said condenser, and

means to rotate said fan whereby condensate from said condenser is intercepted by the fan and distributed onto exposed surfaces within said .vapor space.

vapor space, a fan disposed to rotate in a horizontal plane, below said condenser, and means to rotate said fan whereby condensate from said condenser is intercepted by the fan and 'distributed onto exposed surfaces within said vapor space, the rate of rotation and pitch of the blades of said fan being such that the reaction component on the vapors is at least as high as the normal rate oLrise of the vapors and the rate of rotation, depth of blades and number of blades of said fan being such that essentially all of the condensate from said condenser is intercepted by the fan during rotation.

7. In combination with an evaporator having a portion for holding a body of solution to be distributing the same by centrifugal force onto the wa1ls defining the vapor space. r 8. An apparatus for distributing washing fluid on exposed surfaces of evaporating equipment, which comprises a revolving type spray device mounted to rotate within the vapor space of an evaporator, said rotary spray device extending close to the surfaces of said evaporating equipment and designed to supply washing fluid onto exposed surfaces of said evaporator, and means for supplying washing fluid to said device.

9. An apparatus for distributing washing fluid on exposed surfaces of evaporative equipment, which comprises a revolving fan mounted to rotate horizontally Within the vapor space of an evaporator, said fan being designed to intercept falling drops of washing fluid and deflectthe same centrifugally onto exposed surfaces of said evaporator, means to supply falling particles of washing fluid into said vapor space above said fan, and means for rotating said fan 10. The method of preventing the accumulation of solids on exposed surfaces within evaporative equipment, which comprises condensing within the vapor space of said equipment at least a portion of the vapors produced by evaporation, collecting said condensate as it falls in said vapor space and centrifugally diverting at least a large part of said condensate toward and onto exposed surfaces within said vapor space.

LEROY G. BLACK. 

